Abhishek Bachchan — often looking like a younger, hunkier Alfred Molina — is agreeably earnest as Roshan, the American son of Indian expats who brings his ailing grandmother (Waheeda Rahman) back to her former home in the Chandni Chowk section of Old Delhi.

At first, Roshan maintains the bemused reserve of a curious tourist while noting the idiosyncratic customs and culture of his parents’ homeland. (His habit of snapping photos with his cell phone evolves into a running gag.) He gets into trouble only when he directly involves himself in everyday dramas, such as when he objects to the behavior of a corrupt cop (Vijay Raaz) — and is briefly jailed for his impudence — or when he defies tradition by extending kindness to an “untouchable” street sweeper (Divya Dutta).

Roshan takes a very serious interest in Bittu (sexy, willowy Sonam Kapoor), a local who yearns to enter a nationally televised talent competition — “Slumdog Idol,” anyone? — even as her disapproving father (the ubiquitous Om Puri) plots to limit her options with an arranged marriage. But budding romance is overshadowed by faith-based conflict as long-forgotten disputes between Hindu and Muslim neighbors are reignited by reported sightings of a marauding “mad monkey” thought to be of supernatural origin.

Mehra demonstrates an impressive sense of showmanship during the pic’s musical highlights — a lavish fantasy sequence that transports Delhi residents to Times Square is nothing short of spectacular — and draws winning performances from many members of his cast. Production values are suitably sharp.

But Mehra allows too many distractions to cloud his warts-and-all portrait of a populace united by an exuberant love of life, yet divided by petty disputes and hidebound attitudes. Worse, his tonal gear-shifting in the final third of “Delhi-6” comes too late and too clumsily.

As a result, Mehra simply doesn’t earn the emotional response he obviously wants to his elicit with the gut-punch consciousness-raising of his overwrought climax.